Liquid infusion apparatus

ABSTRACT

An apparatus and method are disclosed for controlling infusion of liquid into a patient using a peristaltic pump. The liquid infusion apparatus includes a liquid conduit having a proximal segment, a distal segment and an intermediate segment. The liquid infusion apparatus also includes a flow valve in fluid communication with the intermediate and distal segments. The flow valve includes a shuttle member slidably disposed within a housing about the distal segment, the shuttle member being configured for lateral movement relative to an elongated axis of the distal segment. The shuttle member is configured to operate in a first configuration to impede fluid flow through the liquid conduit and in a second configuration for which fluid flow through the liquid conduit is unimpeded. The shuttle member includes a resilient grasper for selectively engaging and disengaging a mating actuator resiliently received by the grasper.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/086,902, filed Nov. 2, 2020, which is a divisional of U.S. patentapplication Ser. No. 15/878,669, filed Jan. 24, 2018, now issued as U.S.Pat. No. 10,821,223, which is a continuation of U.S. patent applicationSer. No. 13/923,082, filed Jun. 20, 2013, now issued as U.S. Pat. No.9,878,089, which is a continuation of U.S. patent application Ser. No.12/494,166, filed Jun. 29, 2009, now issued as U.S. Pat. No. 8,469,932,which is a divisional of U.S. patent application Ser. No. 11/271,705,entitled “Liquid Infusion Apparatus,” filed Nov. 10, 2005, now issued asU.S. Pat. No. 7,553,295, the entire contents of each of which areincorporated by reference herein.

FIELD

This invention relates to apparatus for infusing liquid into a patient,and more particularly to such apparatus suitable for operation in amagnetic resonance image (MRI) environment of high magnetic fields andrequired low radiofrequency interference.

BACKGROUND

It is desirable to carefully control the intravenous (IV) administrationof liquids to a patient. Conventional gravity IV solution delivery viacommonly-available IV administration sets is typically not sufficientlyaccurate for the delivery of many types of fluids and drugs. Variouspositive displacement pumping devices have been developed for carefullycontrolling such IV administration. Some types of IV pumps control flowwithin a standard IV administration set via peristaltic (either linearor rotary) pumping schemes directly on the tubing of a conventional IVinfusion set. Other types may incorporate a proprietary volumetriccassette, and still other types utilize a syringe-like device. However,there currently exists no IV controller capable of completely safeoperation within a MRI suite wherein a considerable need exists for thecontrolled delivery of medicinal liquids. Frequently, patients scheduledfor MRI examination arrive at the MRI suite with IV solutions beingadministered and controlled by devices which must be disconnected as thepatient is moved into the suite where high magnetic fields are presentand no outside RF interference can be tolerated.

The basic characteristics of an infusion pump involve the delivery ofmedicinal or nutritional liquids, over time, into the venous system of aliving subject. Certain physical limitations regarding the delivery rateand pressure are elemental in IV liquid-infusion control. IV fluids arepumped at pressures typically in the range of 0.2 to 10 PSI. Theinfusion device should include detection of over-pressure andoperational limits at not more than about 20 PSI. Flow ranges typical ofIV pumps are from 0.1 to 2000 ml/hr. Such specifications forconventional IV infusion apparatus are quite different from thespecifications for injector devices which are often used in radiologicsettings, including MRI, for purposes of very rapid bolus injection ofimage-enhancing contrast agents. Such devices ‘push’ contrast agents atpressures up to 300 PSI and in very short periods of time in contrast toIV drug delivery systems. Contrast agents are solely for imageenhancement and have no medicinal value in a patient and are commonlydelivered using piston or syringe-type pumps that provide the requisitehigh fluid pressures and rapid deliveries.

The high magnetic field surrounding MRI systems can negatively affectthe operation of various devices (including conventional IV controldevices), especially those devices that are constructed with magneticmaterials, and can seriously jeopardize a patient's safety as a resultof devices utilizing magnetic materials that can be attracted at highvelocity into the magnetic field of the MRI system where patient orattendant personnel are located.

Conventional devices for infusing liquids into a patient are typicallysmall portable units often attached to an IV pole holding both theinfusion device and associated liquids to be infused. Such devicesutilize either stepper-type motors or simple DC motors which includemagnetic materials for providing the mechanical power required to drivethe pumping unit. Further, some form of electronic control unit receivesthe manual inputs of prescribed infusion rate settings, and controls thepumping unit to deliver the desired quantity of liquid over time. Suchcontrol unit may emit spurious radio frequency signals as a result ofpoor electrical design or insufficient shielding and are thereforecommonly installed outside an MRI environment and outside the shieldingtherefor.

With the advent of MRI procedures for the imaging of internal bodystructures, very special requirements must be satisfied in the design ofmedical devices intended to be used within the MRI environment. MRIsystems exploit the physical phenomenon of nuclear magnetic resonance(NMR) by which RF stimulation of atomic nuclei within an associatedmagnetic field results in the emission of a small RF ‘spin echo’ fromthe nucleus so stimulated. In the case of patient imaging, hydrogennuclei bound with water are the usual targets for magnetic resonance atselected frequencies. Other molecules and compounds can also be selectedfor study, as in Nuclear Magnetic Spectroscopy, by choosing resonancespecific magnetic field strengths and associated radio frequencies. Forsimplicity the typical hydrogen atom-based MRI image-acquisition processis referred to herein, but it should be recognized that the subjectinvention is equally useful in MRI spectrographic studies at a pluralityof field strengths and frequencies.

The typical MRI system includes several components, as shown in FIG. 1.For example, the operator's console 25, 27 and various processing 37,display 29, 31 and radio frequency and magnetic gradient amplifyingequipment 33, 35 are all located outside of the environment of the MRIscanning suite which must be configured to eliminate image-degradingradio frequency interference and field effects of metallic structuresthat can introduce field distortions and become safety hazards. The MRIscanning unit produces large magnetic and RF fields, and must be capableof receiving the extremely small RF nuclear ‘echoes’, and is thereforetypically located within a shielded room 11. Such rooms greatlyattenuate outside RF noise and may also provide some containment of thescanner's magnetic fields that include both fixed high B field anddynamic fields due to high-field ramping gradients.

However, certain devices are required to be placed in the scan roomeither to assist with care of the patient being imaged or for the use ofattending staff. Of particular interest are those devices which must beplaced in the scan room during the time of image acquisition when thepatient is present and the magnetic fields are ‘up’ and RF reception ofthe tiny nuclear ‘echoes’ must be cleanly acquired. Electrically passivemetallic items such as oxygen bottles or ‘crash carts’ present safetyhazards to the patient due to their potential to be strongly attractedby the magnetic field of the scanner. Such items can be ‘pulled’ intothe imaging volume where the patient is located, creating potential forserious injury or death. Additionally, great effort is made during themanufacture and installation of the scanner/magnet to assure that thelines of flux within the imaging volume are highly homogenous to assurethat acquired images have minimal spatial distortion. Thus, devicesformed of magnetic material that are positioned within the magneticfield of the scanner can introduce distortions into this homogeneousfield and the resultant images. The level of hazard and the degree offield/image distortion due to magnetic materials depends upon thecomposition and location with respect to the imaging volume.

The hazards due to ‘flying’ objects can be controlled to some degree bythe use of non-ferrous devices such as the aluminum oxygen bottle.Additionally, the gravitational weight of some devices or their rigidfixation in the scanning room may be sufficient to overcome the force ofmagnetic attraction on the ferrous mass of such devices toward theimaging volume. However, such devices with some ferrous mass, thoughinhibited from being pulled into the magnetic field, may neverthelessintroduce inhomogeneity in the magnetic field. Distortions in thehomogeneity of the magnetic field within the imaging volume must be keptat such a level as to be of minimal consequence to the operator readingthe resultant image or data. And, the possibility of field distortion isproportionally increased as devices with metallic materials arepositioned closer to the imaging volume, with the most critical positionbeing near the center of the imaging volume, essentially where thepatient is positioned. Additionally, because of the extremely low levelsof RF signals produced by the target image nuclei, great care must betaken to assure that devices with active electronic circuits do not emitspurious RF signals as forms of electronic noise. Such noise can sodegrade the signal-to-noise ratio of signals received by the MRI sensorcoils and receivers that image resolution is reduced or renderedcompletely unreadable. Active circuits must be carefully shielded toassure that their RF emissions are extremely low at the specificfrequencies of the imaging process. Conversely, it is possible throughcareful design, to place a source of RF energy for signal transmission,therapy, or the like, within the MRI environment, but such signals mustbe chosen to avoid the discreet Lamar frequencies unique to theparticular magnetic field strength of a given MRI scanner, and must beof such high spectral purity as to coexist with the MRI without causingany deleterious effects. The intense magnetic fields produced by the MRIscanner can cause detrimental effects on the performance of common DCand stepper motors in devices needed within the MRI scanning room, tothe point of making their control difficult or causing their completefailure. The gradient or time-varying magnetic fields can inducechanging (AC) currents in motors and associated circuitry which may alsocause false motor operation.

For example, injectors of image-enhancing contrast agents are commonlyrequired to inject such contrast agent during actual imagingacquisition, and such devices include motors that contain magneticmaterial and that must therefore be located at a sufficient distance toreduce interactive effects with the magnet of the MRI scanner for properoperation and safety. Controllers and consoles of electronics anddisplays that generate spurious RF signals are therefore located outsidethe MRI scan room to avoid interference with the sensitive RF receiversof the RF scanner.

Accordingly, it is desirable to provide a self-contained, MRI-compatibleinfusion pump for the relatively long term control and delivery of thevarious infusion solutions and drugs routinely delivered to a patientwithin the MRI environment during image acquisition. Such devices mustnot emit any significant RF emissions that might adversely affect imageacquisition operation from within the MRI scan room and must notinteract with the magnetic fields therein either to cause distortion ofthe field or to be influenced by these fields sufficiently to jeopardizereliable operation of such devices.

For various reasons, including cost, safety, convenience, andperformance, it may be desirable to use the MRI-compatible pump only forshort durations while the patient is in the MRI. In this case, thepatient must be disconnected from a non-MRI-compatible pump andconnected to the MRI-safe pump prior to the MRI, and later switchedback. Switching a patient's IV set involves a health risk due tosterility concerns and a cost in medical personnel's time. Additionally,fluid may be wasted from a prescribed volume during the IV-switchprocedure.

Therefore, it is also desirable to provide a method for substituting anMRI-compatible pump for a prior-connected, non-MRI-compatible pump for ashort duration without removing the patient from the original IV set.The MRI-compatible pump may be connected in substitution for theoriginal pump after the original pump is removed. The original pump maybe similarly reconnected, and the MRI-compatible pump removed, after theMRI is complete. By easily interchanging pumps on the same IV setinstalled on a patient, the time and expense of interchanging pumps areminimized, and compromises of the sterility of an IV installation on apatient are minimized.

An IV set commonly includes a length of tubing to extend from a fluidconnector at a source of a liquid to be infused into a patient to afluid connector disposed at a distal end of the tubing for connecting toan intravascular needle. It is desirable to be able to rapidly transfera patient that is begin infused with liquid via a pump that is non-MRIcompatible to a pump that is MRI compatible in preparation of the patentfor MRI procedures, without disconnecting the tubing or removing theneedle from its intravascular function, or other actions which maycompromise sterility or inconvenience the patient.

SUMMARY

In accordance with the illustrated embodiment of the present invention asafe and effective infusion device for use within the MRI scan roomachieves reduction of magnetic material and accurate pumping control aswell as reduction of RF emissions. In one embodiment, the infusiondevice includes an ultrasonic motor that eliminates magnetic materialsand that does not produce any detrimental magnetic fields and that isnot affected by external magnetic fields. The ultrasonic (U/S) motordrives a peristaltic or other suitable fluid pumping mechanism, and isdriven by a multiphasic electronic signal specifically designed toproduce very little RF harmonic noise in the spectral range of about 6or 8 MHz to about 130 MHz in which MRI receivers are most sensitive. Thedrive power for the U/S motor is generated via circuitry which producesmultiphasic drive signals of at least sine and cosine wareforms atrelated ultrasonic frequencies. These drive signals are produced as asinusoidal wave to reduce high frequency harmonic components which maydisturb the MRI's RF-sensitive responsiveness. One scheme for producingthese multiphasic signals uses coreless or “Air Core” transformersconstructed with inherent leakage inductance that interacts with thecomplex impedance of the U/S motor to convert lower voltage square wavesignals at the primary winding into sinusoidal high voltage signals atthe secondary windings suitable for powering the U/S motor and producinglittle harmonic RF interference. Alternatively, D.C. voltages ofopposite polarities can be alternately switched to supply alternatingvoltages. The switched signals can be filtered into sinusoidal signalsand applied to the inputs of high voltage linear amplifiers that are setfor such gain as needed to produce resultant outputs of sufficientvoltage and sinusoidal shape to drive the U/S motor.

Control electronics receive commands through an input keypad for settingprescribed fluid flow rates to be delivered, and such inputs aretranslated into signals to control the U/S motor and pumping mechanism.Various safety devices feed back operational information to the controlelectronics, including detection of motor speed and motion of pumpelements, air bubbles in the fluid path, drip rate, high pressure, lowfluid, low/no flow, overtime, and the like. The present infusion deviceincludes battery power for portability, and is housed in oneRF-shielded, non-magnetic housing for convenient location anywherewithin the MRI scan room without introducing image degrading RFinterference or producing distortions of the homogeneous magnetic field,and without being affected by the strong magnetic fields or RF energyproduced by the MRI system. Such unrestricted placement of the device isof great importance to the safety and convenience of the attending MRIstaff and imaging patient. Further, in the case of a linear peristalticpump mechanism, the particular position of pump elements, along with thespeed of motion of these elements, must be known to the controller. Thedegree to which the controller may modulate speed and control exactpositions of the pump elements directly affects the resolution andaccuracy of the fluid delivery system. To provide a high degree of speedand position accuracy, an optical encoder (801, 802) is installed alongthe main pump shaft. The encoder disk (802) has many small graticulemarks about the circumference, and a single index mark. The opticalsensor (801) detects the marks and produces output signals indicative ofboth the index and individual graticule marks. The index occurs onlyonce each 360 degrees of rotation to facilitate the controller sensingan index to know the position of the pumping elements. The rate at whichthe graticule marks are sensed indicates the speed of the pump shaft aswell as its fine position relative to the index mark. The controllerresponds to the optical encoder to modulate the speed of motion of thepump elements at specific positions of the pump shaft in order to reduceinherent non-linearities in fluid delivery of the linear-typeperistaltic pump. In this way, highly accurate and linear fluid flow maybe achieved.

In an additional embodiment, a method is employed to substitute anMRI-compatible pumping device for a prior-connected, non-MRI-compatiblepumping device while preserving the patient's connection to aprior-connected primary intravenous (IV) infusion set. The patient iscommonly connected to a primary IV set through a primary,non-MRI-compatible pump. Upon arrival at the MRI suite, a secondary,MRI-compatible pump attached to a secondary IV set connects to theprimary IV set to continue actively-pumped IV fluid delivery. Theprimary pump is disengaged from the patient's installed primary IV set,and a flow preventer (to shut off flow) that is standard on most IV setsis activated to inhibit liquid flow through a segment of the primary IVset. The fluid-receiving or proximal end of the secondary IV set isconnected to the upstream end of the primary IV set near the source ofthe IV fluid. The upstream connection may be conveniently formed bypuncturing a conventional “Y” connector on the primary IV set with ahollow needle on the secondary IV set, or via a luer-type “Y” siteconnector. Air is flushed from the secondary IV set by flowing fluidfrom the upstream connection, and the fluid-delivery or distal end ofthe secondary IV set is then connected in similar manner at a downstreamconnection in the primary IV set. Pumping of the liquid may then beresumed using the MRI-compatible pump operating on the secondary IV setwithout having dislodged the intra-vascular needle or actually openingthe primary IV circuit. The patient and MRI-compatible pump may then bemoved close to the MRI scanner while maintaining the controlled IVtherapy. The secondary IV set so employed may simply be disconnected anddiscarded after the MRI procedure, again without opening the originalprimary IV circuit, and the original primary IV set may be reinstalledinto the original, non-MRI-compatible pump while preserving thepatient's connection to the primary IV set. By not opening the fluidcircuit of the primary set, minimal risk to the patient and sterile IVpath are achieved as well as reducing medical waste and cost ofreplacing the primary IV set after the MRI procedure.

To facilitate rapid transitions between primary and secondary pumps andinfusion sets, one embodiment of the present invention includes aninfusion device that receives a liquid conduit for delivering liquid toa patient at volumetric rates that are controllable by the device.Peristaltic pumping of liquid through the conduit installed within thedevice is enabled only upon proper registration of a flow valve within areceptacle of the device for actuation upon closing of a safety door.Flow of liquid through the conduit is inhibited upon opening the safetydoor, and various sensors are incorporated into the device along thepath of the conduit to detect inflow and outflow liquid pressures,available liquid supply, air bubbles in the conduit, and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pictorial plan view of a conventional MRI system showingtypical placement of operational components;

FIG. 2 is a partial perspective view of an infusion device in accordancewith one embodiment of the present invention;

FIG. 3 is a block schematic diagram of the infusion device of FIG. 2;

FIG. 4 is a partial perspective view of the two pumping apparatuses inaccordance with one embodiment of the present pump-substitutioninvention;

FIG. 5 is a flowchart illustrating a method of temporarily substitutinga secondary IV pump for a primary IV pump without removing the patient'sprimary IV set in accordance with the present invention;

FIG. 6 is a flowchart illustrating a method of replacing a secondary IVpump with a primary pump in accordance with the present invention; and

FIG. 7 is a side view of a length of precision tubing in accordance withthe present invention;

FIG. 8 is an exploded top view of valve apparatus in accordance with oneembodiment of the present invention;

FIG. 9 is a top view of the valve apparatus of FIG. 8 in one operatingconfiguration;

FIG. 10 is a top view of the valve apparatus of FIG. 8 in anotheroperating configuration;

FIG. 11 is an exploded side view of operative components in oneembodiment of the present invention;

FIG. 12 is a partial side view of the embodiment of FIG. 11 inassembled, operational configuration;

FIGS. 13A, 13B and 13C comprise a block schematic diagram illustratingoperating components of the illustrated embodiment of the presentinvention;

FIG. 14 is a schematic diagram of drive circuitry for a multiphasic u/smotor in accordance with one embodiment of the present invention;

FIG. 15A is a chart illustrating typical flow rate through a linearperistaltic pump operating at constant speed;

FIG. 15B is a chart illustrating flow rate through a linear peristalticpump operating in compensated manner in accordance with an embodiment ofthe present invention;

FIG. 16 is an exploded perspective view of a pump unit according to thepresent invention;

FIG. 17 is a partial sectional view of a gasket disposed between housingsegments;

FIG. 18 is a partial cross sectional view of annunciator lightsaccording to the present invention; and,

FIG. 19 is a front view of the pump unit of FIG. 16.

DETAILED DESCRIPTION

Issued U.S. Pat. No. 7,404,809 entitled “Non-Magnetic Medical InfusionDevice,” filed on Oct. 12, 2004 by R. Susi, and issued U.S. Pat. No.7,267,661 entitled “Non-Magnetic Medical Infusion Device,” filed on Jun.17, 2002 by R. Susi, are incorporated herein in their entireties by thisreference thereto. Referring now to the plan view in FIG. 1 of an MRIsystem, the scanning room 9 is disposed within shielding boundary walls11, with a control room 13 for operators or attendant personnelpositioned outside the boundaries of the scanning room 9. The scanningroom 9 includes the image acquisition equipment including a source 15 ofintense magnetic field 16 that emanates from the source in substantiallyhomogenous array throughout the adjacent space and around a patient 17.Various components of the system for performing the image acquisitionoperations, including gradient 19 and sensor 21 and RF coils 23 aredisposed about the patient 17 for stimulating the nuclei ‘echos’ to mapthe positions thereof within the spatially-homogenous magnetic field 16as the patient's body is scanned in conventional manner along multipleorthogonal axes. The shielding boundary walls 11 (and ceiling and floor)provide shielding against radio-frequency interference and, asfabricated with ferrous materials, may also establish outer limits ofthe magnetic field distribution around magnetic 15.

The control room 13 is disposed outside the shielding boundary walls 11and is equipped with computer input keyboard 25, computer display 27,monitor 29 of patient's vital life signs, controls 31 for liquidinfusion apparatus, and the like. Such representative equipment ishoused outside the shielding boundary walls 11 to inhibit intrusion ofspurious magnetic and electrostatic and RF signals into the imageacquisition operations within the scanning room 9. Similarly, thegradient amplifiers 33 for amplifying signals from conventional gradientcoils 19-21, along X, Y, and Z coordinates and RF amplifiers 35 and theimage-processing computer 37 are also located outside the shieldingboundary walls 11 for the same reason. The thru-wall interconnections 39between the components within the scanning room 9 and the electronicequipment 25, 27, 29, 31, 33, 35, 37 disposed outside the room 9typically also includes RF filtering to diminish the sources and theportals by which and through which RFI signals may enter the scanningroom 9.

A high-pressure liquid-injection device 41 commonly resides within thescanning room 9 to administer IV injection into the patient 17 of liquidcompositions, for example, that enhance image acquisition (e.g.,contrast medium) or that otherwise provide diagnostic or therapeuticbenefits to the patient 17 being scanned. Such conventional injectiondevice 41 should desirably be positioned close to the patient 17 tofacilitate IV liquid infusion, but must be positioned remotely to avoiddisrupting the homogeneous magnetic field 16, and to minimize RFI andoperational failures of the infusion device 41 resulting from operatingin the intense magnetic field adjacent the patient 17. Control of suchinfusion device 41 may be via remote controller 31 disposed withincontrol room 13.

In accordance with the embodiment of the invention illustrated in FIG.2, an improved liquid infusion device 43 is operable within intensemagnetic fields and with negligible RFI to provide positive displacementof a liquid 45 such as saline or antibiotics, or sedative, or the like,in controlled volumes per unit time. The device does not include anyferrous or magnetic materials, and is substantially shielded againstirradiating any RFI during operation. Specifically, the device 43includes a pump in the lower chamber 47, as later described herein. Thepump chamber 47 receives therein the flexible, resilient tubing 49 thatis pre-packaged and sterilized as a component of a conventional IVliquid infusion set that also includes a conventional drip chamber 51 aspart of the infusion set. Controls for the pump in chamber 47 include anoperator's input keypad 48 that is shielded against radiation of RFI forsetting infusion parameters, and a drip detector 53 that may be disposedabout the drip chamber 51 to detect flow of liquid from the supply 45. Adisplay 53 is positioned in the upper portion of the housing 55 whichmay be formed of non-magnetic, RF-shielding material such asconductively-coated plastic or aluminum, or the like. The housing 55attaches with one or more clamps 57 to a rigid support 59 formed ofnon-magnetic material such as fiberglass or aluminum, or the like.

Referring now to the pictorial block schematic diagram of FIG. 3, thereis shown a peristaltic-type positive-displacement pump 60 disposedwithin the pump chamber 47 of the housing 55 to operate with the lengthof tubing 49 that passes therethrough between the drip chamber 51 andthe patient. The peristaltic pump 60 (linear or rotational) is driven byan ultrasonic motor 64 via appropriate mechanical linkage 65 to actuatea squeeze roller against the tubing 49 in known peristaltic pumpingmanner, or to actuate a series of elements 67 through a lineartubing-squeezing sequence to produce peristaltic pumping action in knownmanner. Various visual and audible annunciators 61 may be provided tosignal operational conditions either within acceptable limits, or withinerror or failure conditions.

A conventional ultrasonic (U/S) driving motor 64 is powered in knownmanner by multiphasic signals applied thereto from the motor drivecircuit 69. A controller 71 for the device includes a central processingunit 73 with associated peripheral components including Random AccessMemory (RAM) 75, Read-Only Memory (ROM) 77, Digital-to-Analog (D/A)converter 79, and an Input/Output channel 81. This controller 71receives input control information from the operator's keypad 48, andreceives feedback information about pump speed from sensor 83 and aboutliquid flow from drip detector 85 disposed about the drip chamber 51. Inresponse to the inputs supplied thereto, the controller 71 operates onstored programs to actuate a display 53 of operating parameters (orother data), and to actuate the motor drive circuit 69 for energizingthe ultrasonic motor 64 for rotation at a controlled speed. A powersupply 63 is connected to the controller 71 and drive circuit 69 tosupply electrical power thereto, and is connected to a battery 87 toreceive electrical power therefrom during stand-alone operation, or toreceive line voltage via plug 63, as required.

In accordance with this embodiment of the present invention, no magneticmaterial is used in any of the components of the infusion device 43including the ultrasonic motor 64, pump 60, power supply 63, controller71 and associated components. Additionally, none of such components isadversely affected during operation by a strong magnetic field. And, anyRF energy that may be generated by electronic signals within theultrasonic motor 64, drive circuit 69, controller 71, power supply 63 orassociated components is specifically shielded by conductive structures91, 93 disposed around such components to inhibit radiation of RFI.Additionally, radio-frequency interference filters 95 are disposed aboutall through-shield conductors to inhibit radiation of RFI through suchportals.

Referring now to FIG. 4, in an additional embodiment of the presentinvention, a method is employed to substitute an MRI-compatible pumpingdevice 406 for a prior-connected, non-MRI-compatible pumping device 430while preserving the patient's 450 connection to a prior-connectedprimary IV infusion set 432. The patient is initially connected 450 tothe primary IV infusion set 432 which is installed in anon-MRI-compatible primary pump 430. The primary pump 430 controls thepumping action in response to information entered into the unit, and inresponse to a sensor 434 that monitors liquid flow. Fluid connectors aredisposed in the primary IV set upstream 400 and downstream 410 of theprimary pump 430. Compatible fluid connectors are also disposed in thesecondary IV set upstream 402 and downstream 408 of the secondary pump406.

Referring now to the flowchart of FIG. 5, a method is illustrated forsubstituting an MRI-compatible pumping device 406 for a prior-connected,non-MRI-compatible pumping device 430 while preserving the connection450 of a prior-connected primary IV infusion set 432 to a patient.Initially, the patient is connected 500 to the primary IV set 432 andprimary pump 430, and liquid is infused 502 into the patient through theprimary IV set 432 and primary pump 430. Before entry of the patientinto the MRI environment, the primary pump 430 is disabled from pumpingliquid, and the flow of liquid through the primary IV set 432 isinhibited via a shut-off mechanism within the primary IV set.

The secondary MRI-compatible pump 406 is configured to operativelyreceive a secondary IV set 404. The secondary pump 406 may include asensor for monitoring liquid flow to control the pumping action.

To transition a patient from a non-MRI-compatible pump 430 to anMRI-compatible pump 406 without altering the primary IV set 432 asinstalled on a patient, the upstream fluid connector 402 of thesecondary IV set 404 is connected 510 to the upstream fluid connector400 of the primary IV set 432. After purging the tubing of air, thedownstream fluid connector 408 of the secondary IV set 404 is connected512 to the downstream fluid connector 410 of the primary IV set 432. Thesecondary IV set is operatively installed 508 into the secondaryMRI-comptabile IV pump 406. In one embodiment, a sensor 434 may beconnected 514 to the pump 406 for measuring the liquid pumped from theliquid source. Liquid is infused 516 into the patient through theconnection 450A of the primary IV set 432 to the patient, and throughthe secondary IV set 404 and secondary pump 406. Because the secondarypump 406 is MRI-compatible, the infusion may continue via the secondarypump 406 within the MRI environment. The primary IV set 432 remainsinstalled on a patient who therefore does not have to be directlyconnected at 450A to the secondary IV set 404, but rather the secondaryIV set 404 “bypasses” the section of the primary IV set 432 that remainsoccluded between connectors 400, 410.

In an additional embodiment, the secondary pump 406 is connected to theprimary IV set 432 before the primary pump 430 is operatively disengagedand removed from the primary IV set 432.

Referring now to the flowchart of FIG. 6, a method is illustrated forremoving the secondary pump 406 and reconnecting the primary pump 430after the patient is removed from the MRI environment. The fluidconnectors 402 and 408 of the secondary IV set 404 are disconnected 600from the fluid connectors 400 and 410 of the primary IV set 432. Thisprevents flow of liquid through the secondary IV set 404. In oneembodiment, the flow through the primary IV set 432 is prevented by ashut-off mechanism disposed in the primary IV set 432 between connectors400 and 410. Such shut-off mechanism may manually cut off fluid viahand-operated slide or roller clamp, or the like. The secondary IV set404 is operatively re-installed removed 602 from the secondary pump 406and is discarded. The primary pump 430 is operatively re-installed onthe primary IV set 432 to which the patient remains connected 450. Theflow sensor 434 may be reconnected to control the rate of liquidinfusion through the primary IV set 432. Liquid is again infused 608into the patient via the primary IV set 432, the primary pump 430 andthe original connection 450 of the primary IV set to the patient.

Referring now to FIGS. 4 and 7, there are shown perspective and sideviews, respectively, of operational aspects of the liquid-deliverysystems in accordance with one embodiment of the present invention.Specifically, a liquid conduit 404 includes a fluid connector 402 at aninput or proximal end, and includes a flanged connector 701 that couplesthe proximal segment of the liquid conduit 404 to an intermediatesegment including a length of precision tubing 703, as later describedherein, that terminates in flow valve 705. A distal segment of the fluidconduit includes a fluid connector 408 at the distal end thereof, and iscoupled at its proximal end to the flow valve 705. The entire assemblyincluding proximal and distal segments of the fluid conduit 404, fluidconnectors 402, 408, flanged connector 701, precision tubing 703 andflow valve 705 is prepared and sterilized and packaged in anhermetically-sealed envelope in a conventional manner for immediateinstallation in the pumping device 406, as needed to infuse liquid intoa patient conveniently during an MRI procedure.

The precision tubing 703 may be formed as a thin-walled extrusion of aflexible, elastic material such as silicone rubber, or otherbiocompatible polymer that confines a selected liquid volume per unitlength within the bore of selected cross-sectional dimension between theflanged connector 701 and the flow valve 705. In this way, progressiveperistaltic pumping by successive pinching and advancing of the pinchpoint along the tubing 703 toward the flow valve 705 administers a knownvolume of liquid to a patient. The length of tubing 703 between flangedcoupling 701 and flow valve 705 may be slightly stretched into positionwithin the pumping device 406 to provide resilient engagement of theflanged connector 701 and flow valve 705 within their respective matingreceptacles 706, 708 disposed at opposite ends of the active peristalticpumping mechanism of the device 406.

The flow valve 705, as illustrated in the exploded top view of FIG. 8,includes an outer housing 707 within which the precision tubing 703passes. The mating receptacle 708 in the pumping device 406 for thehousing 707 includes a complementary recess that receives the housing707 in only one orientation and secures the properly-installed housingin place with the aid of slight tension exerted thereon by tubing 703. Aslide or shuttle element 710 is disposed within the housing 707 to slidelaterally relative to the elongated axis of the tubing 703, with thetubing 703 passing through a tapered aperture in the shuttle element710. Thus, with the shuttle element 710 fully depressed within thehousing 707, the tubing 703 passes through the portion of the apertureof maximum cross sectional dimension, leaving the bore of the tubing 703fully open for unimpeded flow of liquid therethrough. In alternateposition of the shuttle element 710 maximally protruding from thehousing 707, the tubing 703 is pinched within a portion of minimalcross-sectional dimension of the aperture, as shown, to inhibit liquidflow through the tubing 703. Thus, as initially installed within thepumping device 406, the flow valve 705 is configured to inhibit flowthrough the liquid conduit 404 to ensure no inadvertent dosing of apatient until the pumping device 406 is rendered fully operational.

In accordance with one embodiment of the present invention, the device406 is inhibited from administering liquid to a patient until a liquidconduit 404 is properly installed and an access door 407 is fully closedand safely latched shut. The access door 407 carries passive componentsof interlocking elements that properly engage and interface with activecomponents of the device 406 for proper operation only with the accessdoor 407 fully closed and safely latched shut. The region of the device406 that is accessed through the opened access door 407 includes agenerally vertical channel for receiving the flanged connector 701 in acomplementary receptacle 706 that is positioned above the peristalticpumping mechanism 712. A sensor may be disposed above the receptacle forthe flanged connector to optically sense presence of liquid in theproximal portion of the conduit 404, and operate to inhibit the pumpingdevice 406 from further pumping activity in response to sensing an emptyconduit.

The access door 407 carries an upper platen 716 that cooperates with apressure sensor 717 disposed behind a flexible membrane 711 andintermediate the receptacle 706 for the flanged connector 701 and theperistaltic pumping mechanism 712 to position an initial length ofinstalled tubing 703 between spaced platen 716 and pressure sensor 717.In this way, the pressure at which liquid is supplied to the device canbe tonometrically determined within the precision tubing 703, orotherwise measured, for use in correcting calculation of pumpingactivity required to deliver a selected volumetric infusion rate ofliquid to a patient.

Similarly, a platen 718 is carried on the access door 407 at a locationaligned with another pressure sensor 719 disposed intermediate thepumping mechanism 712 and the flow valve 705. In the manner, similar tooperation of pressure sensor 717, the pressure sensor 719 and platen 718confine the precision tubing 703 to provide tonometric measurement, orother measurement, of outlet pressure. An upper limit of outlet pressuremay be selected to trigger an alarm condition if such liquid outletpressure exceeds the set limit as an indication of a clogged outletconduit.

The access door 407 also carries a platen 721 positioned in alignmentwith the peristaltic pumping mechanism 712 to confine the precisiontubing 703 therebetween to effect linear peristaltic pumping activity inthe generally downward direction from inlet pressure sensor 717 towardoutlet pressure sensor 719. Neither pressure sensing nor pumpingactivity may proceed until the access door 407 is fully closed toposition the associated platens about the precision tubing 703 forproper sensing and pumping operations.

The access door 407 also carries a detent element 723 that mates with aresilient clamp 725 carried on the shuttle element 710 of flow valve705. Specifically, these mating elements effect sliding movement of theshuttle element 710 from initially protruding position (i.e., tubing 703pinched) toward fully open position (i.e., tubing 703 not pinched) asthe access door is closed, as illustrated in FIG. 9. Additionally, theengaged detent element 723 and resilient clamp 725 remain engaged as theaccess door 407 is initially opened, thereby to pull the shuttle element710 toward maximum protrusion from the housing 707 to pinch tubing 703and inhibit further liquid flow therethrough, as illustrated in FIG. 10.The attachment of the resilient clamp 725 carried on the shuttle element710 of flow valve 705, and the detent element 723 carried on the accessdoor 407 is overridden and resiliently released following maximumprotrusion of the shuttle element 710 and further opening of the accessdoor 407. Of course, detent element 723 may be carried on the shuttleelement 710, and a resilient clamp 725 may be carried on the access door407 to effect similar interaction and safety operation.

An ultrasonic or optical sensor may be disposed within the device 406 ata location thereon below the flow valve 705 and about the distal segmentof the liquid conduit 404 to detect the presence of air bubbles in theoutlet conduit (that is formed of ultrasonically oroptically-transmissive material). This sensor may include a protrudingU-shaped receptacle for receiving the conduit therein and for supportingoptical elements in the protruding arms of the receptable to sensebubbles in liquid passing therebetween in the outlet flow of liquidwithin the conduit. A mating U-shaped element 407 is supported on theaccess door 711 in alignment with the U-shaped receptacle of the bubbledetector to capture the liquid conduit 404 fully recessed therein inorder to fully close the access door 407.

Referring to the partial side view of FIG. 12, there is shown a partialside view of the components of FIG. 11 assembled into operationalconfiguration. Specifically, the access door 407 disposed in closedconfiguration positions the platens 716, 718, 721 on one side of theintermediate length of precision tubing 703 against the respectivesensors 717, 719 and pumping mechanism 712. The flow valve 705 isconfigured to open condition and liquid is pumped through the conduit404, 703 in response to rotation of the cam shaft 727 of the peristalticpumping device 712. In this manner, pinch points along the precisiontubing 703 progress downwardly as successive pump elements 729 of thepumping device 712 are manipulated by the rotating cam shaft 727 toprovide the peristaltic pumping action in known manner.

Referring now to FIGS. 13A, 13B and 13C there is shown a block schematicdiagram of the operational components of the fluid delivery systemaccording to one embodiment of the present invention. The peristalticpump includes pumping elements or fingers 729 that are manipulated in apumping sequence in response to rotation of the shaft 727. The outputshaft of ultrasonic (U/S) motor 800 is coupled to the pump shaft 727that carries an optical encoder disk 802. The optical sensing element801 detects peripheral marks and an index mark for producing outputsindicative of disk position and speed of rotation. These outputs aresupplied to the controller 71 that also receives control signals frommanual-entry keyboard 48 and from pressure sensors 717, 719, bubbledetector 718 and access door safety switch 716. The controller 71generates multiphasic drive signals via drive circuit 69 and, amongother functions, also controls the display 53, alarm indicators, and thelike.

For proper operation, the linear peristaltic pump mechanism requires ahigh degree of control in order to assure accuracy and linearity offluid flow rate. The operating speed of the pump shaft is modulated toovercome flow-rate non-linearities or discontinuities commonlyexperienced within a peristaltic pumping cycle, as illustrated in thechart of FIG. 15A, of fluid flow rate over time at constant shaft speed.For this reason, the controller 71 requires signal informationindicative of the exact location of pump elements during the interval ofa pumping cycle in order to determine requisite speed modulation andwhen to apply the speed modulation during a pumping cycle. FIG. 15Ashows the uncompensated flow output of the peristaltic pump according toone embodiment operating at a very slow RPM rate, over slightly morethan one revolution (one cycle of 12 pump fingers) that takes about 31minutes and delivers about 0.32 ml of fluid. It should be noted thatthere exists a no-flow “dead band” of approximately 11 minutes in the 31minute cycle, including a small discontinuity. The discontinuity isdependent on very small mechanical tolerances such as the lengths of thefingers, the perpendicularity of the platen to the fingers, and thelikes which vary pump to pump. However, the long 11-minute dead band isvery similar pump to pump.

In accordance with the present invention, very fine control of pump-flowcharacteristics is established utilizing modulation of the rotationalspeed during each cycle of the peristaltic mechanism. The resultantflow, as illustrated in the graph of FIG. 15B resembles the smoothnessand linearity of syringe-fine pumps, a desirable characteristic wheninfusing potent drugs or infusing small patients, i.e., babies.

Specifically, FIG. 15B shows the flow output of the pump resulting fromspeed ‘modulation’ applied to each rotation, in accordance with thepresent invention. The rotational speed modulation is accomplishedusing, for example, 8 discrete different speeds of the motor and pumpduring the dead band interval. To accomplish such speed modulation forflow correction, the drive motor 800 must be able to start and stop veryquickly and in very small angular displacement typically in the rangefrom about 3 to about 10 milliseconds, and within about 0.3 to about 0.9degrees of arc. The encoder 801, 802 outputs of index and 1000 pulsesper revolution indicate to the controller 71 the starting position ofthe dead band (index plus mechanical offset by number of pulses counted)for compensation and the exact (i.e., the rotational distance as pulsescounted) to control timing and application of the discrete speeds. Aftercompensation is applied in this way, according to the present invention,the flow output of the linear peristaltic pump is very linear indelivering very precise amounts of fluid of about 1 ml/Hr. The lowestpump rate (1 ml/HR) is a basis for compensation as at high speeds thedead band is inherently shorter and less consequential.

The optical encoder 801, 802 provides both fine and coarse outputindications of the disk position and speed of rotation. Specifically,one index mark is sensed to identify the exact angular position of thepump shaft 727, and numerous peripheral graticule marks (e.g., 1000about the periphery) provide fine indication of angular re-positioningof the shaft relative to the index mark. Of course, the frequency ofrecurrence of sensed graticule marks also indicates rotational orangular speed of shaft 727. Thus, the controller 71 receives controlsignals from the optical encoder 801, 802 that facilitate modulation ofmotor speed in the manner as described above to overcome discontinuitiesor anomalies in a selected flow rate of fluid through the peristalticpump as illustrated in FIG. 15B, during portions of the pump cycledriven by the ultrasonic motor 800.

In order to accomplish fine resolution of fluid flow rates through theperistaltic pump, the drive motor 800 must be able to start and stopvery rapidly, typically within the range of about 3 to 10 milliseconds.The driving ultrasonic signals are generated by the drive circuit 69 atabout 43 KHz with very low harmonic content in the range of about 6 or 8MHz to about 130 MHz within which MR scanners are sensitive to RFsignals. This is accomplished on the drive circuit 69, as shown in theschematic diagram of FIG. 14, using a shift-register type of counter 70that receives input from voltage-controlled oscillator 72 to generatehigh-voltage ultrasonic frequencies in sine and cosine relationship 74,76. Coreless or air core transformers 78, 80 are driven push-pullthrough field-effect power transistors that receive paired outputs fromthe register 70. The primary inductance (through the turns ratio) andthe leakage inductance of these transformers 78, 80 coact with thecharacteristic input capacitance 82, 84 of the ultrasonic motor 800 toproduce substantially sinusoidal, high-voltage drive signals 74, 76 oflow harmonic content. These sinusoidal drive signals also passefficiently through the filters 95 from the electrically shieldedcontroller section 86 to the electrically shielded motor section 88, andexhibit concomitant low to negligible RF interference attributable todrive signal harmonics.

It should be noted that the ultrasonic motor 800 provides an AC signal90 representative of the composite sine and cosine drive signals. ThisAC signal 90 is rectified and integrated or low-pass filtered to producea DC voltage level 92 that is indicative of motor speed, and isdistinguishable from the position and rotational speed indicationsdigitally derived from the optical encoder 801, 802. The analog DCvoltage level 92 is applied via the operational amplifier 98 to thevoltage-controlled osullator 72 in order to control the frequency of themotor drive signals. Specifically, the rotational speed of theultrasonic motor 800 varies inversely with frequency of the drivesignals. Accordingly, an applied ‘motor run’ signal 94 in combinationwith the DC feedback voltage 92 and the time constant of the R and Cfilter 96, cause the drive circuit 69 to generate drive signals 74, 76that sweep in frequency from a slightly higher initial frequency that isuseful for starting the motor 800 from standstill to an appropriaterunning frequency that establishes a steady-state motor speed.

Alternatively, the drive signals, 74, 76 for the ultrasonic motor 800may be generated from combined signals Q1/Q3, and Q2/Q4 through suitablefiltering to generate low voltage sinusoidal sine and cosine signals.These signals may then be amplified to sufficient level (typically about100 Volts RMS) to drive the ultrasonic motor 800.

Referring now to FIG. 16, there is shown an exploded perspective view ofone embodiment of the pump unit 406 of the present invention in which agasket 806 is disposed between mating segments 805, 807 of the housing.The gasket 806 is formed of a flexible and electrically conductivematerial to form a fluid-tight seal between the housing segments 805,807 as shown in the sectional view of FIG. 17. The conductive gasket 806also inhibits internally-generated RF noise signals from radiating outof the conductive housing segments 805, 807. The conductive housingsegments 805, 807 thus form an integral shield that prevents radiativeelectronic signals from emanating from internal circuitry, for exampleas illustrated in FIG. 13, and additionally protects such internalcircuitry from fluid spills that might be detrimental to reliableoperation.

Referring now to the sectional view of FIG. 18, there is shown one lightsource such as light-emitting diode 804 of a plurality of such lightsources and different colors that are lineally disposed within thehousing segment 805 near a top edge thereof. These light sources arepositioned behind the door 711 of conductive material that is hinged 730along an outer edge of the housing segment 805 to facilitate easy accessto the peristaltic pumping structure that is supported therein. The door711 includes a locking lever 733 for securely closing the door 711 inoperational position against a length of tubing 703, as illustrated andpreviously described herein with reference to FIG. 7. The door 711 alsoincludes a clear or translucent window 810, as illustrated in FIGS. 18,19, in alignment with the light sources 804 to provide large-areaillumination for easy visualization from a distant location of the lightfrom a source 804. A light-scattering element or light pipe 812 may bedisposed intermediate the light sources 804 and the window 810 toprovide more uniform illumination over the area of the window 810 inknown manner. Thus, a light source 804 of green color may pulse on andoff recurring during normal pumping operation, and a light source of redcolor may pulse on and off recurring to indicate an alarm condition, allfor convenient visualization from a distant location. And the lightsources 804 are sufficiently recessed within the conductive housingsegment 805 to inhibit radiative RF noise signals from emanating fromthe housing.

Therefore, the liquid infusion apparatus of the present inventionpromotes easy replacement or substitution of pumping devices withoutinterrupting patient connection or otherwise comprising sterility of aninstalled infusion system. An infusion set includes integral segments ofa liquid conduit and operable components for interaction and operationalengagement with associated components of a pumping device that iscompatible with an MRI environment. Ultrasonic motor drive signals aregenerated with low harmonic content using efficient step-up transformerthat co-act with the characteristic input impedance of the ultrasonicmotor to shape signals as sinusoidal waveforms of low harmonic content.

1. (canceled)
 2. A liquid infusion apparatus, comprising: an ultrasonic motor configured to provide displacement of a liquid from a liquid source through a liquid conduit; an oscillator that generates an output at a frequency; a circuit connected to receive the output from the oscillator to produce recurring output pulses at spaced intervals on a plurality of output terminals; and a resistor-capacitor (RC) filter with an associated time constant, the RC filter configured to cause sweeping of the frequency of the output of the oscillator when a motor control signal indicates that the ultrasonic motor is to start running.
 3. The liquid infusion apparatus of claim 2, further comprising a feedback signal that provides an indication of the operation of the ultrasonic motor.
 4. The liquid infusion apparatus of claim 3, wherein the feedback signal operates in combination with the RC circuit to cause sweeping of the frequency of the output of the oscillator.
 5. The liquid infusion apparatus of claim 3, wherein the feedback signal is indicative of motor speed.
 6. The liquid infusion apparatus of claim 2, wherein the ultrasonic motor provides displacement of the liquid through the liquid conduit in a linear manner.
 7. The liquid infusion apparatus of claim 2, wherein the sweeping of the frequency of the output of the oscillator is from a higher frequency to a lower frequency.
 8. The liquid infusion apparatus of claim 7, wherein the higher frequency is useful for starting the motor from a standstill and the lower frequency is an appropriate frequency to establish a steady-state motor speed.
 9. The liquid infusion apparatus of claim 2, wherein the displacement of the liquid through the liquid conduit provides a constant fluid flow rate.
 10. The liquid infusion apparatus of claim 2, wherein the liquid infusion apparatus is compatible with an MRI environment.
 11. The liquid infusion apparatus of claim 2, further comprising a conductive housing that inhibits internally-generated RF noise signals from radiating out of the infusion apparatus.
 12. A liquid infusion apparatus, comprising: an ultrasonic motor configured to provide displacement of an IV fluid from a source of the IV fluid through a liquid conduit; a voltage-controlled oscillator that generates an output at a frequency; a drive circuit connected to receive the output from the voltage-controlled oscillator to produce recurring output pulses at spaced intervals on a plurality of output terminals; and a resistor-capacitor (RC) filter with an associated time constant, the RC filter configured to facilitate sweeping of the frequency of the output of the voltage-controlled oscillator when a motor control signal indicates that the ultrasonic motor is to start running.
 13. The liquid infusion apparatus of claim 12, further comprising a feedback signal that provides an indication of the operation of the ultrasonic motor.
 14. The liquid infusion apparatus of claim 13, wherein the feedback signal operates in combination with the RC circuit to cause sweeping of the frequency of the output of the voltage-controlled oscillator.
 15. The liquid infusion apparatus of claim 13, wherein the feedback signal is indicative of motor speed.
 16. The liquid infusion apparatus of claim 12, wherein the ultrasonic motor provides displacement of the IV fluid through the liquid conduit in a linear manner.
 17. The liquid infusion apparatus of claim 12, wherein the sweeping of the frequency of the output of the voltage-controlled oscillator is from a higher frequency to a lower frequency.
 18. The liquid infusion apparatus of claim 17, wherein the higher frequency is useful for starting the motor from a standstill and the lower frequency is an appropriate frequency to establish a steady-state motor speed.
 19. The liquid infusion apparatus of claim 12, wherein the displacement of the liquid through the liquid conduit provides a constant fluid flow rate.
 20. The liquid infusion apparatus of claim 12, wherein the liquid infusion apparatus is compatible with an MRI environment.
 21. The liquid infusion apparatus of claim 12, further comprising a conductive housing that inhibits internally-generated RF noise signals from radiating out of the infusion apparatus. 